Tube furnace for heating

ABSTRACT

A heating furnace for gases or liquids characterized in that a radiant section and a convection section are located, respectively, in the upper and lower spaces inside the furnace, the radiant section and the convection section being separated from each other by a heat-insulating reflecting plate which is formed with passages for combustion gas, pipes disposed in a zigzag or coiled fashion are vertically suspended in the radiant section and a plurality of downwardly directed burners are mounted on the ceiling and the sidewalls of the radiant section, the pipes in the radiant section being communicated at one ends with the end of pipes disposed in the convection section and led at the other ends out of the furnace through the ceiling, and an exhaust port for the flue gas is formed open through the lower part or through a side of the convection section.

United States Patent 721 Inventors Takehiko Sato Yokkaichi; Saburo Fukui, Hiroshima, both of Japan [211 App]. No. 53,178 [22] Filed July 8, 1970 [45] Patented Dec. 28, 1971 g [73] Assignees Mitsubishi Jukogyo K.K.; Mitsubishi Petrochemical K.K.

' Tokyo, Japan [32] Priority July 17, 1969 [33'] Japan [31] 44/56630 [54] TUBE FURNACE FOR HEATING 4 Claims, 2 Drawing Figs.

[52] US. Cl 122/356 [51] lnt.Cl F22b 21/24 [50] Field of Search 122/355, 356, 510

[5 6] References Cited UNlTED STATES PATENTS 3,230,052 1/1966 Lee et a1. 122/356 X Primary Examiner Kenneth W. Sprague Attorney-George B. Oujevolk ABSTRACT: A heating furnace for gases or liquidscharacterized in that a radiant section and a convection section are located, respectively, in the upper and lower spaces inside the furnace, the radiant section and the convection section being separated from each other by a heat-insulating reflecting plate which is formed with passages for combustion gas, pipes disposed in a zigzag or coiled fashion are vertically suspended in the radiant section and a plurality of downwardly directed burners are mounted on the ceiling and the sidewalls of the radiant section, the pipes in the radiant section being communicated at one ends with the end of pipes disposed in the convection section and led at the other ends out of the furnace through the ceiling, and an exhaust port for the flue gas is formed open through the lower part or through a side of the convection section.

TUBE FURNACE FOR HEATING BACKGROUND OF THE INVENTION This invention relates to a tube furnace for heating, particularly a tube furnace for heating which performs principally the pyrolysis of hydrocarbons, particularly of ethane, propane, naphtha, kerosene, light oil, gas oil and the like, into olefins, diolefins, aromatic hydrocarbons and the like.

In the past, one type of furnaces widely in use for this purpose is the so-called horizontal tube furnace or a heating furnace of the construction in which a large number of shortflame burners are arranged through the sidewalls of the furnace, and a nest of pipes are horizontally supported in the center of the radiant section consisting of the sidewalls, ceiling, bed and front and rear walls, and a convection section for the recovery of waste heat located above the radiant section. In the furnace of the type described, short-flame burners of flat flames must be used for uniform heating of the pipes and for keeping the flames from direct contact with the pipes. In addition, the relatively small capacity of the individual burners necessitates the use of a large number of burners, thus adding complicacies to the operation and maintenance of the equipment to disadvantage. The short-flame burners use mainly gaseous fuels in order to hold the flat flames and avoid damaging of the pipes due to scatter of sludge. This not only puts extreme restrictions to the use of less expensive fuels such as heavy oil and other oils as cracking residues but also tends to cause clogging of the burner tips with impurities in the fuel or deformation of the burner tiles due to coking of the fuel oil, which in turn can affect the flame shape and induce local overheating of the pipes. Further, it is often the case with a furnace of this type that the horizontal pipes wave or sag because of creep strain or deformation by thermal stress, accompanied by corresponding defonnation or damaging of the pipe fittings.

Another variety of conventional furnaces consists of a bed, sidewalls, a ceiling, and front and rear walls which altogether constitute a radiant section, a plurality of burners arranged on the bed and sidewalls, a nest of pipes suspended vertically in the center of the radiant section, and a convection section for the recovery of waste heat that is located above and alongside the radiant section. Since the furnace of this construction employs upwardly directed long-flame burners and vertically suspended pipes, it is advantageous over the first variety of conventional furnaces above mentioned in respect of the capacity and quantity of the burners and because of less possibilities of deformation and damage of the pipe fittings. However, the upwardly directed burners may cause coking of the burner tiles and, in extreme cases, they may even lead to poor distribution and leakage of the fuel oil out of the furnace with the danger of catching fire. The suspended pipes render it difficult to provide the convection section of the furnace immediately above the radiant section and, therefore, the convection section must be located alongside or above and along the radiant section. Thus if the pressure inside the furnace is increased the flames in the radiant section are attracted toward the direction of the flue of the convection section. This is a frequent cause of damage, local overheating or uneven heating of the heat transfer pipes of the convection section. Among other disadvantages of the conventional furnaces are high erection cost and inconvenience in operation and maintenance due to the fact that the heavy convection section is located at the furnace top.

SUMMARY OF THE INVENTION An object of the invention is to provide a new vertical tube furnace for heating which is free of the foregoing disadvantages of the conventional furnaces.

Another object of the invention is to provide a vertical tubetype heating furnace which attains higher product yields than by conventional equipment of this type and which is, moreover, economical and easy to operate, maintain and control.

Another object of the invention is to provide the furnace construction such that a radiant section and a convection section' are defined, respectively, in the upper and lower parts of the furnace, the two sections being separated by a heat-insulating reflecting plate formed with passages therethrough, and pipes or a nest of pipes are vertically suspended in the radiant section, and a plurality of downwardly directed burners are arranged through the ceiling and sidewalls, and an exhaust port for the flue gas is formed open in the lower part or alongside the convection section.

A further object of the invention is to provide a heating furnace has extensive applications not merely for the pyrolysis of hydrocarbons but as a chemical reaction furnace for effecting endothermic reactions.

Now a preferred embodiment of the heating furnace of the invention will be described hereunder in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a section on the line 1-1 inFIG. 2 of a tube furnace for heating according to this invention.

FIG. 2 is a section on the line II--II in FIG. I.

DETAIL OF THE INVENTION Throughout the FIGS., numeral 1 designate the framework of the furnace body, and 2 designates sidewalls of the furnace body that are combined with front and rear walls 3, a ceiling 4, a bed 5, and a heat-insulating reflecting plate 6 to constitute a radiant section 7. Along the section of the radiant section 7 that connects the vertical bisectors of the front and rear walls there are suspended a nest of vertical pipes 8 in zigzag or coiled fashion inside the radiant section by means of hangers 10 which are equipped with spring hunger 9 and disposed through the ceiling 4. Said spring hunger 9 has a operation to be absorb thermal-deformation of pipes 8. A plurality of flat flame-shaped burners 11 are provided through the ceiling 4 and are so positioned as to give off as long downward flames as possible along the side walls 2. Also, along a horizontal line in the middle part of the sidewalls, there are a plurality of flat flame-shaped burners 12 which are adapted to produce downwardly directed flames along and close to the sidewalls, thereby to cooperate with the ceiling burners 11 to heat the sidewalls 2 to a red hot state, so that the nest of pipes 8 can be uniformly heated by the heat of radiation from the sidewalls 2 and the burner flames. To facilitate the installation of the sidewall burners 12, the portions near the middle parts of the sidewalls has shoulder-portion 13 as shown in FIG. 1, though it is not essential where the requirements for heating the sidewalls as above stated are met adequately. Between the heat-insulating reflecting plate and the bed 5 there are formed a plurality of gas passages 14, through which combustion gas from the radiant section 7 flows down into the convection section 15. The convection section 15 is defined by opposing sidewalls 16, front and rear walls 3, the heat-insulating reflecting plate 6, and bottom plate 17. In the upper space of the convection section there are provided, horizontally in a zigzag or coiled fashion, pipes 18 for preheating material hydrocarbons in communication with the inlet end of the nest of pipes of the radiant section 7. Beneath the preheating pipes are laid water pipes 19 in a similar arrangement. Said water pipe 19 has a operation for preheat a water to be fed to a quick cooling heat exchanger 24. The furnace is also provided with a flue 20 for the combustion gas, an exit 21 for waste gas, an inlet port 22 for material hydrocarbons, and an outlet 23 for the pyrolyzed gas, which communicates to a quick cooling heat exchanger 24 mounted on the furnace top above the ceiling 4 of the convection section.

In the heating furnace of the above construction, the hydrocarbons to be processed are charged through the inlet port 22 of the convection section into the preheating pipes 18, and, as it passes through the pipes, the charge is heated through heat exchange with the waste combustion gas from the radiant section 7 to an optimum temperature for the initiation of pyrolysis. The charge then flows up and down in a zigzag fashion through the vertical pipes 8 of the radiant section 7, while being rapidly heated mainly by the heat of radiation sections and one convection section.

6. Because the burners are mounted high, the chance of any heavier-than-air combustible gas finding its way from the outside into direct contact with the flames inside the furnace is from the sidewalls 3 heated to a red hot state by the ceiling li d M hi h d g f f t i d, and sidewall burners 12 as as by the long downward An example of ethylene pyrolysis with a heating furnace in flames f those burners and thereby p p s the conformity with this invention will be given below. pyrolytic reaction as desired. The resultant is flown through The heating furnace used was a vertical tube furnace plpe oimet 24 mto Subsequent components such as the bodying the invention consisting of a furnace body 2.9 meters q coolmg heat exchanger on the other the wide, 4.7 meters long, and 9.6 meters high. It had l2 flat bustlon from the fiat long'flame burners F m the flame-shaped burners through the ceiling and 10 such burners f Sectlon 7 fl downward k the t of Plpes 8 and the through the sidewalls. ln this furnace was pyrolyzed naphtha sidewalls 2, into the convection section through the having a Specific gravity of 07012 (at 5/ 0 c) and a mean Passages 14 formed between the heat-Insulating reflectmg molecular weight of 98. The starting material in this case was Plate: 6 i the bed After h exchange of heat the P 15 treated at the rate of 6,200 kg. of naphtha per hourwith 3,200 P P 18 and Water P P 19, it is led through the flue kg. of steam per hour. By the flat burners a heat amount of 20 and finally exhausted out 35 from a Stack not Show 4.3X l O KcalIh was supplied to the radiant section so that the With the construction described above, the tube furnace for pipe inlet in the radiant section could be maintained at 560 C. heating in accordance with this invention has a number of adand the outlet temperature of the furnace at 840 C. As the vantages as enumerated below: 20 result, the composition of a pyrolyzed gas tabled below was 1. Even if burners of increased capacity are used, the flames obtained. For the burners a mixed fuel consisting of 50 perin the radiant section form parallel flows with the nest of Cent grade C heavy oil and 50 Percent ethylenetecovered pipes, thus avoiding direct contact of the flames with the nest Waste g composed P p lly f hydrogen and methane was of pipes. Therefore, the number of burners required may be employeti C5 frac,- Ci-Ci nonarom. arom, frac. below Component H2 CH4 02H; C2H4 Ci irao, Ci frac. trac. B.P. 180 0. Others Weight, percent 1.2 16. 4 0. 33 29. 5 16.2 7. 77 13. 3 11.41 Balance.

reduced and w-sludge fue]s of low combustion rate a for Note: l.The proportions ol'the composition were calculated on the dry gas basis.

2. frac. means fraction 3. arom. means aromatic fraction example grade C heavy oil and other inexpensive liquid fuels 4, means boning poi, may be employed. This not merely saves the installation cost it will be obvious to those skilled in the art that various but, in addition, permits steam blowing of the burner tips, changes may be made in the invention without departing from thereby rendering it possible to operate and maintain the fur the spirit and scope thereof and therefore the invention is not nace advantageously. limited by that which is illustrated in the drawing and 2- in h b rn r r in ll i h h iP directed described in the specification, but only as indicated in the acdownward, the fuel even if poorly distributed will drop inside 40 companying claims. the furnace with no possibility of depositing on the burner tiles What is claims is: and forming coke thereon. Also, the fuel even if allowed to l. A tube furnace for heating characterized in that a radiant leak out of the furnace has no danger of catching fire. section and a convection section are located, respectively, in

3. The radiant section of the furnace is surrounded by heatthe upper and lower spaces inside the furnace, the radiant secinsulating ceiling, bed and side walls and also by the heat-insu tion and the convection section being separated from each lating reflecting plate. Moreover, the downwardly directed other by a heat-insulating reflecting plate which is formed with long-flame burners achieve uniform radiant heat distribution. passages for combustion gas, pipes are vertically suspended in These features combine to minimize the possibilities of local h ra ian i n an a plurality f downwardly recte overheating and coking and maintain good r a tion ondiburners are mounted on the ceiling and the sidewalls of the tions. Where the reaction pipes are filled with a catalyst, the radiant section, the pipes in the radiant section being commulifetime of the catalyst can be prolonged. nicated at one ends with the end of pipes disposed in the con- 4. The arrangement of the convection section underneath vection section and led at the other ends out of the furnace the radiant section and the provision of adequate passages for through the ceiling, and an exhaust port for. the flue gas is combustion ga between the heat-in lating refle ting l t formed open through the lower part of the convection section. and the bed enable the furnace to have a rectifying effect of A tube furnace for heating according to clalm 1 Where"! the combustion gas. In addition, because the combustion gas Said burners are Provided Such that a flame of its flow at P uniformly flows downward, uneven heating in the convection lel direction to Said P P section due to any drift convection can be avoided and the A tube furnace for heating accordfng to l 1 wherem product i ld i di l increased, said pipes are disposed in a zigzag or coiled fashion.

5. The relatively heavy convection section being installed at A fumaCP for heating according to clalm twherem a low place, it is easy to build and maintain. Additional adthe water P P whlch Preheat to be fed a q t Coolvantage is obtained from the viewpoint of the furnace layout if lng heat f i are PP f Sectlon at the convection section is provided below and alongside the beneath Said P p disposed Convection Section radiant section so that the furnace is composed of two radiant 

1. A tube furnace for heating characterized in that a radiant section and a convection section are located, respectively, in the upper and lower spaces inside the furnace, the radiant section and the convection section being separated from each other by a heat-insulating reflecting plate which is formed with passages for combustion gas, pipes are vertically suspended in the radiant section and a plurality of downwardly directed burners are mounted on the ceiling and the sidewalls of the radiant section, the pipes in the radiant section being communicated at one ends with the end of pipes disposed in the convection section and led at the other ends out of the furnace through the ceiling, and an exhaust port for the flue gas is formed open through the lower part of the convection section.
 2. A tube furnace for heating according to claim 1 wherein said burners are provided such that a flame of its flow at parallel direction to said pipes.
 3. A tube furnace for heating according to claim 1 wherein said pipes are disposed in a zigzag or coiled fashion.
 4. A tube furnace for heating according to claim 1 wherein the water pipes which preheat water to be fed to a quick cooling heat exchanger are provided in connection section at beneath said pipes disposed in convection section. 